A method of this type is discussed in the publication “Adaptive Cruise Control System—Aspects and Development Trends” by Winner, Witte, Uhler and Lichtenberg, Robert Bosch GmbH, in the SAE Technical Paper Series 961010, International Congress & Exposition, Detroit, Feb. 26-29, 1996. The control system discussed in this publication, also known as an ACC system (adaptive cruise control), is based on a distance sensor, e.g. a radar sensor having multiple-target capability, which is mounted on the front side of the vehicle in order to measure distances to and relative speeds of preceding vehicles. As a function of the measurement data of this radar system, the speed of a driver's vehicle is then controlled in such a manner that a predefined distance, which the driver is able to determine in the form of a so-called setpoint time gap, is maintained to the immediately preceding vehicle. If there is no preceding vehicle in the locating range of the radar, control is carried out to a desired speed set by the driver.
For example, normally this system intervenes, via a throttle valve, in the drive system of the vehicle so that the vehicle speed is regulated via the drive torque of the engine. However, when, for example, on downhill grades, or when, necessitated by distance, a stronger deceleration of the vehicle may be necessary, the drag torque of the engine is not adequate to bring about a sufficient deceleration of the vehicle, then an intervention in the braking system of the vehicle is carried out.
To permit a stable control and to avoid adversely influencing the comfort or driving safety, the control system should react with the shortest possible delay time to the control commands output to the drive system or braking system. However, upon activation of the vehicle brake, a certain delay in response results due to the fact that the wheel brake cylinders and the remaining components of the hydraulic braking system have a certain dead volume which may need to first of all be filled with brake fluid before the brakes at the individual wheels of the vehicle actually become effective.
German Published Patent Application No. 196 15 294 relates to a device for controlling the braking force at the wheels of a vehicle, in which prior in time to the actual pressure buildup necessary for adjusting the required braking torque, a small braking pressure in the form of a time-restricted fill pulse is fed into the braking system. Here, the fill pulse is generated individually for the wheel brakes of the individual wheels as a function of movement variables of the vehicle, particularly as a function of a system deviation of the lateral acceleration of the vehicle and its time derivation. German Published Patent Application No. 34 23 063 relates to a traction control system for vehicles, in which a small braking pressure is fed as a function of the change in the throttle valve position, as a function of the vehicle speed or as a function of slip thresholds which lie below the response threshold for the actual traction control.